1. Field of the Invention
Example embodiments of the present invention relate to a platen assembly, an apparatus having the platen assembly and a method of polishing a wafer using the same. More particularly, example embodiments of the present invention relate to a platen assembly for inducing a polishing pad to uniformly polish a wafer, an apparatus having the platen assembly and a method of uniformly polishing a wafer using the platen assembly.
2. Description of the Related Art
In general, a circuit pattern for a semiconductor device is formed through various unit fabrication processes such as a deposition process, a photolithography process, an etching process, an ion implantation process, a polishing process, a cleaning process and a drying process that are performed sequentially and repeatedly. Among the above unit processes for semiconductor device fabrication, the polishing process plays an important role in increasing the degree of integration and in improving structural and electrical reliability of a semiconductor device. The chemical mechanical polishing (CMP) process has become widely employed as a polishing process for manufacturing a semiconductor device. In the CMP process, a thin layer on a wafer is planarized by a chemical reaction between a slurry and the thin layer and by a mechanical friction between a polishing pad and the thin layer.
A conventional apparatus for performing the CMP process (hereinafter, referred to as “CMP apparatus”) includes a polishing pad, a platen for supporting the polishing pad, a polishing head to which a wafer is secured, a slurry reservoir from which the slurry is supplied to the polishing pad, and a pad conditioner for improving the quality of the polishing pad. The wafer is rotated on a central axis of the polishing head, and the polishing pad makes contact with the rotating wafer, so that a thin layer present on the wafer is polished by the chemical reaction and mechanical friction between the thin layer on the wafer and the polishing pad.
An example of the conventional CMP apparatus is disclosed in U.S. Pat. No. 6,607,425. This apparatus includes ring-shaped bladders and a pressure membrane on a platen, and each of the bladders is pressurized individually.
FIG. 1 is a view that schematically illustrates a structure of a conventional CMP apparatus. Referring to FIG. 1, the conventional CMP apparatus 1 includes a polishing belt 10 that is circulated by a roller (not shown) so as to polishing a wafer W and a polishing head 20 to which the wafer W is secured and by which the wafer W makes contact with the polishing belt 10. In addition, the conventional CMP apparatus also includes a platen 30 for supporting the polishing belt 10, a plurality of ring-shaped bladders 40 positioned on the platen 30 and a pressure membrane 50 for pressurizing the polishing belt 10 through the bladders 40.
In the conventional CMP apparatus, when a CMP process is performed on the wafer, a peripheral portion of the wafer can be polished to a much larger degree than a central portion thereof due to the pressure distribution of the polishing head 20. That is, a the amount of material removed at the peripheral portion of the water W during the CMP process is much larger than that the amount of material removed at the central portion of the wafer W. To compensate for this difference, the width of the bladder 40 can be made to be larger at the peripheral portion of the platen 30 than at the central portion of the platen 30, thereby minimizing the difference in the amount of material polished between the peripheral portion and the central portion of the wafer W.
The bladders 40 are positioned adjacent to each other in the above conventional CMP apparatus, so that a pressure variation in a first bladder 40 can affect the pressure of second bladders 40 adjacent to the first bladder 40. Hence, the conventional CMP apparatus is limited in that it is difficult uniformly polish the wafer despite the efforts described above to compensate for the difference in the amount of material polished between the central portion and peripheral portion thereof.